Resilient well cement compositions and methods

ABSTRACT

The present invention provides improved compositions and methods for sealing pipe in a well bore. The compositions which harden into highly resilient solid masses having high strengths are basically comprised of a hydraulic cement, an aqueous rubber latex, an aqueous rubber latex stabilizing surfactant and silica hydrophobicized with silicon oil.

BACK GROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to cementing subterraneanwells, and more particularly, to cement compositions which set intoresilient solid masses having high strength.

[0003] 2. Description of the Prior Art

[0004] Hydraulic cement compositions are commonly utilized in primarycementing operations whereby pipe strings such as casings and liners arecemented in well bores. In performing primary cementing, a hydrauliccement composition is pumped into the annular space between the walls ofthe well bore and the exterior surfaces of the pipe string disposedtherein. The cement composition is permitted to set in the annular spacethereby forming an annular sheath of hardened substantially impermeablecement therein. The cement sheath physically supports and positions thepipe string in the well bore and bonds the exterior surfaces of the pipestring to the walls of the well bore whereby the undesirable migrationof fluids between zones or formations penetrated by the well bore isprevented.

[0005] The development of wells including one or more laterals toincrease production has recently taken place. Such multi-lateral wellsinclude vertical or deviated (including horizontal) principal well boreshaving one or more ancillary laterally extending well bores connectedthereto. Drilling and completion equipment has been developed whichallows multi-laterals to be drilled from a principal cased and cementedwell bore. Each of the lateral well bores can include a liner cementedtherein which is tied into the principal well bore. The lateral wellbores can be vertical or deviated and can be drilled into predeterminedproducing formations or zones at any time in the productive life cycleof the well.

[0006] In both conventional single bore wells and multi-lateral wellshaving several bores, the cement composition utilized for cementingcasing or liners in the well bores must develop high strength aftersetting and also have sufficient resiliency, i.e., elasticity andductility, to resist the loss of the bonds between the pipe andformation and the cement composition. Also, the cement composition mustbe able to resist cracking and/or shattering as a result of pipemovements, impacts and shocks subsequently generated by drilling andother well operations. The bond loss, cracking or shattering of the setcement allows leakage of formation fluids through at least portions ofthe well bore or bores which can be highly detrimental.

[0007] The cement sheath in the annulus between a pipe string and thewalls of a well bore often fail due to pipe movements which cause shearand compressional stresses to be exerted on the set cement. Such stressconditions are commonly the result of relatively high fluid pressuresand/or temperatures inside the cemented pipe string during testing,perforating, fluid injection or fluid production. The high internal pipepressure and/or temperature results in the expansion of the pipe string,both radially and longitudinally, which places stresses on the cementsheath causing it to crack or causing the cement bonds between theexterior surfaces of the pipe or the well bore walls, or both, to failwhich allows leakage of formation fluids, etc.

[0008] Stress conditions also result from exceedingly high pressureswhich occur inside the cement sheath due to the thermal expansion offluids trapped within the cement sheath. This condition often occurs asa result of high temperature differentials created during the injectionor production of high temperature fluids through the well bore, e.g.,wells subjected to steam recovery or the production of hot formationfluids from high temperature formations. Typically, the pressure of thetrapped fluids exceeds the collapse pressure of the cement and pipecausing leaks and bond failure. Other compressional stress conditionsoccur as a result of outside forces exerted on the cement sheath due toformation shifting, overburden pressures, subsidence and/or tectoniccreep.

[0009] Thus, there are needs for improved well cement compositions andmethods whereby after setting, the cement compositions form highlyresilient solid masses which have high compressive, tensile and bondstrengths sufficient to withstand the above described stresses withoutfailure.

SUMMARY OF THE INVENTION

[0010] The present invention provides improved cement compositions andmethods for sealing pipe in well bores which meet the needs describedabove and overcome the deficiencies of the prior art. The improvedcompositions of the invention are basically comprised of a hydrauliccement, an aqueous rubber latex present in an amount in the range offrom about 40% to about 55% by weight of hydraulic cement in thecomposition, an effective amount of an aqueous rubber latex stabilizingsurfactant, and silica hydrophobicized with silicon oil present in anamount in the range of from about 0.5% to about 2% by weight of thecomposition.

[0011] The improved methods of this invention for cementing pipe in awell bore are comprised of the following steps. A cement composition ofthe invention is prepared which hardens into a highly resilient solidmass having high compressive, tensile and bond strengths. The cementcomposition is placed in the annulus between the pipe and the walls ofthe well bore and then allowed to harden therein.

[0012] It is, therefore, a general object of the present invention toprovide improved cement compositions which harden into resilient solidmasses having high strength and methods of using such cementcompositions for sealing pipe in well bores.

[0013] Other and further objects, features and advantages of the presentinvention will be readily apparent to those skilled in the art upon areading of the description of preferred embodiments which follows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] As mentioned, the present invention provides improvedcompositions and methods for cementing pipe in well bores whereby thehardened cement composition is a highly resilient solid mass having highcompressive, tensile and bond strengths and which effectively withstandspipe movements due to expansion, contraction, impacts, shocks or thelike. The compositions of this invention are basically comprised of ahydraulic cement, an aqueous rubber latex, an aqueous rubber latexstabilizing surfactant and silica which has been hydrophobicized withsilicon oil.

[0015] A more preferred composition of this invention is comprised of ahydraulic cement, an aqueous rubber latex, an aqueous rubberlatex-stabilizing surfactant, an epoxy resin, an epoxy resin hardeningagent and porous precipitated silica which has been hydrophobicized withsilicon oil.

[0016] A variety of hydraulic cements can be utilized in accordance withthe present invention including those comprised of calcium, aluminum,silicon, oxygen and/or sulfur which set and harden by reaction withwater. Such hydraulic cements include Portland cements, pozzolanacements, gypsum cements, high aluminum content cements, silica cementsand high alkalinity cements. Portland cements or their equivalence aregenerally preferred for use in accordance with the present invention.Portland cements of the types defined and described in API SpecificationFor Materials And Testing For Well Cements, API Specification 10, 5thEdition, dated Jul. 1, 1990 of the American Petroleum Institute areparticularly suitable. Preferred API Portland cements include classes A,B, C, G and H, with API classes G and H being more preferred and class Gbeing the most preferred.

[0017] A variety of well known rubber materials which are commerciallyavailable in aqueous latex form, i.e., aqueous dispersions or emulsions,can be utilized in accordance with the present invention. For example,natural rubber (cis-1,4-polyisoprene) and most of its modified types canbe utilized. Synthetic polymers of various types can also be usedincluding nitrile rubber, ethylene-propylene rubbers (EPM and EPDM),styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), butylrubber, neoprene rubber, cis-1,4-polybutadiene rubber and blends thereofwith natural rubber or styrene-butadiene rubber, high styrene resin,silicone rubber, chlorosulfonated polyethylene rubber, crosslinkedpolyethylene rubber, epichlorohydrin rubber, fluorocarbon rubber,fluorosilicone rubber, polyurethane rubber, polyacrylic rubber andpolysulfide rubber. The aqueous latex forms of one or more of the aboverubbers can be utilized with the other components of the sealingcomposition being added directly to the latex.

[0018] Of the various aqueous rubber latexes which can be utilized,those formed of cis-polyisoprene rubber, nitrile rubber,ethylene-propylene rubber, styrene-butadiene rubber, nitrile-butadienerubber, butyl rubber and neoprene rubber are generally preferred.

[0019] The most preferred aqueous rubber latex for use in accordancewith this invention is a styrene-butadiene copolymer latex emulsionprepared by emulsion polymerization. The aqueous phase of the emulsionis an aqueous colloidal dispersion of the styrene-butadiene copolymer.The latex dispersion usually includes water in an amount in the range offrom about 40% to about 70% by weight of the latex, and in addition tothe dispersed styrene-butadiene particles, the latex often includessmall quantities of an emulsifier, polymerization catalysts, chainmodifying agents and the like. The weight ratio of styrene to butadienein the latex can range from about 10%:90% to about 90%:10%.

[0020] Styrene-butadiene latexes are often commercially produced asterpolymer latexes which include up to about 3% by weight of a thirdmonomer to assist in stabilizing the latex emulsions. The third monomer,when present, generally is anionic in character and includes acarboxylate, sulfate or sulfonate group. Other groups that may bepresent on the third monomer include phosphates, phosphonates orphenolics. Non-ionic groups which exhibit stearic effects and whichcontain long ethoxylate or hydrocarbon tails can also be present.

[0021] A particularly suitable and preferred styrene-butadiene aqueouslatex contains water in an amount of about 50% by weight of the latex,and the weight ratio of styrene to butadiene in the latex is about25%:75%. A latex of this type is available from Halliburton EnergyServices of Duncan, Oklahoma, under the trade designation “LATEX 2000™.”

[0022] The aqueous rubber latex utilized is generally included in thecement compositions of this invention in an amount in the range of fromabout 40% to about 55% by weight of hydraulic cement in thecompositions.

[0023] In order to prevent the aqueous latex from prematurelycoagulating and increasing the viscosity of the sealing compositions, aneffective amount of a rubber latex stabilizing surfactant can beincluded in the compositions. A suitable such surfactant has the formula

R—Ph—O(OCH₂CH₂)_(m)OH

[0024] wherein R is an alkyl group having from about 5 to about 30carbon atoms, Ph is phenyl and m is an integer in the range of fromabout 5 to about 50. A preferred surfactant in this group is ethoxylatednonylphenol containing in the range of from about 20 to about 30 molesof ethylene oxide.

[0025] Another latex stabilizing surfactant which can be used has thegeneral formula

R₁(OR₂)_(n)SO₃X

[0026] wherein R₁ is selected from the group consisting of alkyl groupshaving from 1 to about 30 carbon atoms, cycloalkyl groups having 5 or 6carbon atoms, C₁-C₄ alkyl substituted cycloalkyl groups, phenyl, alkylsubstituted phenol of the general formula

(R₃)_(a)ph—

[0027] wherein Ph is phenyl, R₃ is an alkyl group having from 1 to about18 carbon atoms and a is an integer of from 1 to 3, and phenyl-alkylgroups wherein the alkyl groups have from 1 to about 18 carbon atoms andthe phenyl-alkyl groups have a total of from about 8 to about 28 carbonatoms; R₂ is a substituted ethylene group of the formula

—CH₂CH₂R₄

[0028] wherein R₄ is selected from hydrogen, methyl, ethyl or mixturesthereof; n is a number from 0 to about 40 provided that when R₁ isphenyl or alkyl substituted phenyl, n is at least 1; and X is anycompatible cation.

[0029] Another latex stabilizing surfactant which can be utilized is asodium salt having the general formula

R₅—Ph(OR₆)₀SO₃X

[0030] wherein R₅ is an alkyl radical having in the range of from 1 toabout 9 carbon atoms, R₆ is the group —CH₂CH₂—, o is an integer fromabout 10 to about 20 and X is a compatible cation.

[0031] Another surfactant which can be utilized is a sodium salt havingthe formula

R₇(OR₈)_(P)SO₃X

[0032] wherein R₇ is an alkyl group having in the range of from about 5to about 20 carbon atoms, R₈ is the group —CH₂CH₂—, p is an integer inthe range of from about 10 to about 40 and X is a compatible cation. Apreferred surfactant of this type is the sodium salt of a sulfonatedcompound derived by reacting a C₂-C₁₅ alcohol with about 40 moles ofethylene oxide (hereinafter referred to as an “ethoxylated alcoholsulfonate”) which is commercially available under the name “AVANELS400™” from PPG Mazer, a division of PPG Industries, Inc. of Gurnee,Ill.

[0033] While different rubber latex stabilizers and amounts can beincluded in the cement compositions of this invention depending on theparticular aqueous rubber latex used and other factors, the latexstabilizer is usually included in the cement compositions in an amountin the range of from about 10% to about 20% by weight of the aqueousrubber latex in the compositions.

[0034] A variety of hardenable epoxy resins can be utilized in thecement compositions of this invention. Preferred epoxy resins are thoseselected from the condensation products of epichlorohydrin and bisphenolA. A particularly suitable such resin is commercially available from theShell Chemical Company under the trade designation “EPON®RESIN 828.”This epoxy resin has a molecular weight of about 340 and a one gramequivalent of epoxide per about 180 to about 195 grams of resin. Anothersuitable epoxy resin is an epoxidized bisphenol A novolac resin whichhas a one gram equivalent of epoxide per about 205 grams of resin.

[0035] For ease of mixing, the epoxy resin utilized is preferablypre-dispersed in a non-ionic aqueous fluid. A non-ionic aqueousdispersion of the above described condensation product ofepichlorohydrin and bisphenol A is commercially available from the ShellChemical Company under the trade designation “EPI-REZ®-3510-W-60.”Another non-ionic aqueous dispersion of an epoxy resin comprised of acondensation product of epichlorohydrin and bisphenol A having a highermolecular weight than the above described resin is also commerciallyavailable from the Shell Chemical Company under the trade designation“EPI-REZ®-3522-W-60.” The above mentioned epoxidized bisphenol A novolacresin is commercially available in a non-ionic aqueous dispersion fromthe Shell Chemical Company under the trade designation“EPI-REZ®-5003-W-55.” Of the foregoing non-ionic aqueous dispersions ofepoxy resins, the aqueous dispersion of the condensation product ofepichlorohydrin and bisphenol A having a molecular weight of about 340and a one gram equivalent of epoxide per about 180 to about 195 grams ofresin is the most preferred.

[0036] The epoxy resin utilized is preferably included in the cementcompositions of this invention in an amount in the range of from about5% to about 15% by weight of hydraulic cement in the compositions.

[0037] A variety of hardening agents, including, but not limited to,aliphatic amines, aliphatic tertiary amines, aromatic amines,cycloaliphatic amines, heterocyclic amines, amidoamines, polyamides,polyethyleneamines and carboxylic acid anhydrides can be utilized in thecompositions of this invention containing the above described epoxyresins. Of these, aliphatic amines, aromatic amines and carboxylic acidanhydrides are the most suitable.

[0038] Examples of aliphatic and aromatic amine hardening agents aretriethylenetetraamine, ethylenediamine, N-cocoalkyltri-methylenediamine,isophoronediamine, diethyltoluenediamine, andtris(dimethylaminomethylphenol). Examples of suitable carboxylic acidanhydrides are methyltetrahydrophthalic anhydride, hexahydrophthalicanhydride, maleic anhydride, polyazelaic polyanhydride and phthalicanhydride. Of these, triethylenetetraamine, ethylenediamine,N-cocoalkyltri-methylenediamine, isophoronediamine,diethyltoluenediamine and tris(dimethylaminomethylphenol) are preferred,with isophoronediamine, diethyltoluenediamine andtris(dimethylaminomethylphenol) being the most preferred.

[0039] The hardening agent or agents utilized are preferably included inthe cement compositions of this invention in an amount in the range offrom about 10% to about 30% by weight of epoxy resin in the compositions(from about 1% to about 3% by weight of hydraulic cement in thecompositions).

[0040] It has been discovered that the addition of particulate silicahydrophobicized with silicon oil, i.e., polydialkylsiloxanes, to thecement compositions of this invention significantly improves thestrengths of the hardened cement compositions, i.e., the compressive,tensile and shear bond strengths of the compositions. The particulatesilica can be hydrophobicized by spraying it with a uniform coating ofsilicon oil followed by heating the sprayed silica to a temperature inthe range of from about 300° F. to about 570° F. for a time period inthe range of from about 1 hour to about 20 hours. Suitable commerciallyavailable silicon oils which can be utilized include the silicon oilwhich is commercially available under the trade designation “SWS 101™”from the Dow Corning Company or the silicon oil commercially availableunder the trade designation “L-45™” from the Union Carbide Corporation.

[0041] While various forms of silica can be utilized, porousprecipitated silica is preferred. Porous precipitated silica can beprepared by adding sulfuric acid and a sodium silicate solution to waterin a reaction vessel with high agitation. The mixture of acid, sodiumsilicate and water must be mixed at a high rate to prevent the formationof low pH areas where gelation will occur. Since silica dissolves toform silicate at a pH value above about 9, smaller particles arecontinuously dissolved during the precipitation process and therefore,uniform particle sizes are obtained. As the silica precipitationprogresses, the small particles aggregate through siloxane bridges toform three dimensional networks that resist the high capillary pressurethat develops during drying. After drying, the precipitated poroussilica is sprayed with silicon oil as described above. Thehydrophobicized silica is included in the cement compositions of thisinvention in an amount in the range of from about 0.5% to about 2% byweight of the hydraulic cement in the compositions.

[0042] A preferred composition of the present invention is comprised ofa hydraulic cement, an aqueous rubber latex present in an amount in therange of from about 40% to about 55% by weight of hydraulic cement inthe composition, an effective amount of an aqueous rubber latexstabilizing surfactant, and silica hydrophobicized with silicon oilpresent in an amount in the range of from about 0.5% to about 2% byweight of hydraulic cement in the composition.

[0043] A more preferred composition of this invention is comprised of ahydraulic cement, preferably Portland cement or the equivalent thereof;an aqueous styrene-butadiene latex which contains water in an amount ofabout 50% by weight of the latex and has a weight ratio of styrene tobutadiene in the latex of about 25%:75%, the latex being present in anamount in the range of from about 44% to about 53% by weight ofhydraulic cement in the composition; an aqueous rubber latex stabilizingsurfactant comprised of an ethoxylated alcohol sulfonate present in anamount in the range of from about 10% to about 15% by weight of theaqueous rubber latex in the composition; an epoxy resin comprised of thecondensation product of epichlorohydrin and bisphenol A present in anamount in the range of from about 10% to about 12% by weight ofhydraulic cement in the composition; an epoxy resin hardening agentcomprised of diethyltoluenediamine present in an amount in the range offrom about 10% to about 20% by weight of epoxy resin in the composition(from about 1% to about 2% by weight of hydraulic cement in thecomposition); and porous precipitated silica hydrophobicized withsilicon oil present in an amount in the range of from about 0.5% toabout 1% by weight of hydraulic cement in the composition.

[0044] The improved methods of the invention for cementing pipe in awell bore are comprised of the steps of preparing a cement compositionof this invention which hardens into a resilient solid mass having highstrength as described above, placing the cement composition in theannulus between a pipe and the walls of a well bore and allowing thecement composition to harden therein.

[0045] In order to further illustrate the compositions and methods ofthe present invention, the following examples are given.

EXAMPLE

[0046] A first cement composition was prepared by combining 424.4 gramsof an aqueous styrene-butadiene latex which contained 50% by weightwater and had a weight ratio of styrene to butadiene of about 25%:75%with 45.6 grams of an aqueous rubber latex stabilizing surfactantcomprised of an ethoxylated alcohol sulfonate. 800 grams of PremiumClass G cement were added to the mixture of latex and stabilizer, andthe resulting cement composition was vigorously mixed for 35 secondsafter which it was cured at 140° F. for 72 hours. A second cementcomposition was prepared which was identical to the first compositiondescribed above except that 8 grams of porous precipitated silicahydrophobicized with silicon oil were combined with the composition. Thesecond cement composition was also mixed for 35 seconds and cured at140° F. for 72 hours. A third composition identical to the firstcomposition described above was prepared except that 4 grams of thehydrophobicized silica were added to the composition. The thirdcomposition was also mixed and cured at 140° F. for 72 hours.

[0047] A fourth cement composition was prepared by combining 353.7 gramsof the aqueous styrene-butadiene latex described above with 38 grams ofthe latex stabilizer described above. To that mixture, 800 grams ofPremium Class G cement, 78.1 grams of an epoxy resin comprised of thecondensation product of epichlorohydrin and bisphenol A and 10.9 gramsof an epoxy resin hardening agent comprised of diethyltoluenediaminewere added. The fourth cement composition was vigorously mixed for 35seconds and then cured at 140° F. for 72 hours. A fifth cementcomposition identical to the above described fourth composition wasprepared except that 8 grams of hydrophobicized silica was added to thecomposition prior to when it was mixed and cured at 140° F. for 72hours. A sixth composition identical to the fourth composition wasprepared except that 4 grams of hydrophobicized silica were added to thecomposition prior to when it was mixed and cured at 140° F. for 72hours. A seventh cement composition identical to the fourth cementcomposition described above was prepared except that a bisphenol Anovolac epoxy resin was substituted for the condensation product ofepichlorohydrin and bisphenol A and 9.1 grams of diethyltoluenediaminehardening agent were included in the composition. The seventhcomposition was also mixed and cured at 140° F. for 72 hours. An eighthcement composition was prepared which was identical to the seventhcomposition described above except that 8 grams of hydrophobicizedsilica were added to the composition prior to when it was mixed andcured at 140° F. for 72 hours. A ninth cement composition which was alsoidentical to the seventh composition was prepared except that 4 grams ofhydrophobicized silica were added to the composition prior to when itwas mixed and cured at 140° F. for 72 hours.

[0048] Cured samples of the nine cement compositions described abovewere used to measure the mechanical properties of the compositions. Thatis, the confined and unconfined compressive strengths of samples weredetermined in accordance with the procedure set forth in the APISpecification For Materials And Testing for Well Cements, APISpecification 10, 5th Edition, dated Jul. 1, 1990 of the AmericanPetroleum Institute.

[0049] In addition, samples of the nine compositions were cured in theannuluses of pipe assemblies, i.e., small pipes centered inside largerpipes. The samples were cured in the pipe assemblies at 140° F. for 72hours. After curing, the shear bond strength of each composition wasdetermined by supporting the larger pipe and applying force to thesmaller inner pipe. The shear bond strength is the total force applieddivided by the bonded surface area which breaks. Additional samples ofthe nine cured compositions were tested for Brazilian tensile strength.

[0050] The results of these tests are given in the Table below. TABLECement Composition Strength Tests Cement¹, Epoxy Shear CompressiveStrength, psi Latex² and Resin and Bond 250 psi 500 psi TensileComposition Latex Hydrophobicized Hardening Strength, ConfiningConfining Strength, No. Stabilizer³ Silica Agent⁶ psi UnconfinedPressure Pressure psi 1 Yes No No 107 587 1043 1420 100 2 Yes Yes No 187653 1119 1358 104 3 Yes Yes No 145 645 1085 1335 112 4 Yes No Yes⁴ 160878 1333 1731 107 5 Yes Yes Yes⁴ 125 1033  1511 1913 172 6 Yes Yes Yes⁴143 940 1461 1788 152 7 Yes No Yes⁵ 160 1045  1496 1804 116 8 Yes YesYes⁵ 186 894 1365 1733 165 9 Yes Yes Yes⁵ 186 886 1341 1678 137

[0051] From the above Table, it can be seen that the test compositionscontaining hydrophobicized silica had improved compressive strengths,shear bond strengths and tensile strengths. Also, it can be seen thatthe compositions including both hydrophobicized silica and hardenedepoxy resin had significantly higher compressive strengths, shear bondstrengths and tensile strengths.

[0052] Thus, the present invention is well adapted to carry out theobjects and advantages mentioned as well as those which are inherenttherein. While numerous changes may be made by those skilled in the art,such changes are encompassed within the spirit of this invention asdefined by the appended claims.

What is claimed is:
 1. An improved cement composition which hardens intoa resilient solid mass having high strength comprising: a hydrauliccement; an aqueous rubber latex present in an amount in the range offrom about 40% to about 55% by weight of hydraulic cement in saidcomposition; an effective amount of an aqueous rubber latex stabilizingsurfactant; and silica hydrophobicized with silicon oil present in anamount in the range of from about 0.5% to about 2% by weight ofhydraulic cement in said composition.
 2. The composition of claim Iwherein said aqueous rubber latex is selected from the group ofcis-polyisoprene rubber, nitrile rubber, ethylene-propylene rubber,styrene-butadiene rubber, nitrile-butadiene rubber, butyl rubber andneoprene rubber.
 3. The composition of claim 1 wherein said aqueousrubber latex is an aqueous styrene-butadiene latex.
 4. The compositionof claim 3 wherein said aqueous styrene-butadiene latex contains waterin the amount of about 50% by weight of said latex and the weight ratioof styrene to butadiene in said latex is about 25%:75%.
 5. Thecomposition of claim 1 wherein said aqueous rubber latex stabilizingsurfactant is an ethoxylated alcohol sulfonate present in an amount inthe range of from about 10% to about 20% by weight of said aqueousrubber latex in said composition.
 6. The composition of claim 1 whereinsaid hydraulic cement is Portland cement or the equivalent thereof. 7.The composition of claim 1 which further comprises an epoxy resin and anepoxy resin hardening agent.
 8. The composition of claim 7 wherein saidepoxy resin is selected from the group of a condensation reactionproduct of epichlorohydrin and bisphenol A and an epoxidized bisphenol Anovolac resin and is present in an amount in the range of from about 5%to about 15% by weight of hydraulic cement in said composition.
 9. Thecomposition of claim 7 wherein said hardening agent is at least onemember selected from the group of aliphatic amines, aromatic amines andcarboxylic acid anhydrides and is present in an amount in the range offrom about 10% to about 30% by weight of epoxy resin in saidcomposition.
 10. An improved cement composition which hardens into aresilient solid mass having high strength comprising: a hydrauliccement; an aqueous styrene-butadiene latex which contains water in anamount of about 50% by weight of said latex and the weight ratio ofstyrene to butadiene in said latex is about 25%:75%, said latex beingpresent in an amount in the range of from about 44% to about 53% byweight of hydraulic cement in said composition; an aqueous rubber latexstabilizing surfactant comprised of an ethoxylated alcohol sulfonatepresent in an amount in the range of from about 10% to about 15% byweight of said aqueous rubber latex in said composition; an epoxy resincomprised of the condensation product of epichlorohydrin and bisphenol Apresent in an amount in the range of from about 10% to about 12% byweight of hydraulic cement in said composition; an epoxy resin hardeningagent comprised of diethyltoluenediamine present in an amount in therange of from about 10% to about 20% by weight of epoxy resin in saidcomposition; and porous precipitated silica hydrophobicized with siliconoil present in an amount in the range of from about 0.5% to about 1% byweight of hydraulic cement in said composition.
 11. The composition ofclaim 10 wherein said hydraulic cement is Portland cement or theequivalent thereof.
 12. An improved method of cementing pipe in a wellbore comprising the steps of: (a) preparing a cement composition whichhardens into a resilient solid mass having high strength comprised of ahydraulic cement, an aqueous rubber latex, an aqueous rubber latexstabilizing surfactant and silica hydrophobicized with silicon oil; (b)placing said cement composition in the annulus between said pipe and thewalls of said well bore; and (c) allowing said cement composition toharden.
 13. The method of claim 12 wherein said aqueous rubber latex insaid cement composition is selected from the group of cis-polyisoprenerubber, nitrile rubber, ethylene-propylene rubber, styrene-butadienerubber, nitrile-butadiene rubber, butyl rubber and neoprene rubber. 14.The method of claim 12 wherein said aqueous rubber latex in said cementcomposition is an aqueous styrene-butadiene latex present in an amountin the range of from about 40% to about 55% by weight of hydrauliccement in said composition.
 15. The method of claim 14 wherein saidaqueous styrene-butadiene latex contains water in the amount of about50% by weight of said latex and the weight ratio of styrene to butadienein said latex is about 25%:75%.
 16. The method of claim 12 wherein saidhydraulic cement in said composition is Portland cement or theequivalent thereof.
 17. The method of claim 12 wherein said compositionfurther comprises an epoxy resin and an epoxy resin hardening agent. 18.The method of claim 17 wherein said epoxy resin in said composition isselected from the group of a condensation reaction product ofepichlorohydrin and bisphenol A and an epoxidized bisphenol A novolacresin and is present in an amount in the range of from about 5% to about15% by weight of hydraulic cement in said composition.
 19. The method ofclaim 17 wherein said hardening agent in said composition is at leastone member selected from the group of aliphatic amines, aromatic aminesand carboxylic acid anhydrides and is present in an amount in the rangeof from about 10% to about 30% by weight of epoxy resin in saidcomposition.
 20. The method of claim 12 wherein said silicahydrophobicized with silicon oil in said composition is present in anamount in the range of from about 0.5% to about 2% by weight ofhydraulic cement in said composition.